First step in controlling a Heart-Lung machine with a computer

1. Automation of
Cardiopulmonary
Bypass
An Autopilot for the Heart-Lung
Machine
Kenneth Wilkerson

2. Theme
 Improving the safety of open-heart surgery
through automation of the heart-lung
machine

3. What is Cardiopulmonary Bypass?
 Removing heart & lungs from circulation
 Used during open heart surgery
 Heart stopped, opened
 E.G.:
 Coronary Artery Bypass Graft
 Valve repair/replacement
 Function taken over by a machine

4. What is a Heart-Lung Machine?
 Replaces function of heart and lungs
 Pump blood
 Oxygenate blood
 Set/maintain body temperature
 Other secondary functions

5. What is a Heart-Lung Machine?
 Key parts for primary purpose:
 Venous reservoir
 Arterial pump
 Heat exchanger
 Oxygenator
 Arterial filter
 Arterial-Venous (A-V) circuit

6. Key parts of heart-lung machine A-V Circuit

7. Early Heart-lung Machine

8. Modern Heart-Lung Machine

9. How is HLM operated?
 Manually
 Constantly monitored by a perfusionist
 Reservoir level
 Arterial line pressure
 Other
 Perfusionist also recording data
 Some sites automated

10. Attempts at automating
 1953 first successful use of HLM
 Within a few years attempt automating
 Measuring reservoir level
 Controlling pump based on reservoir level
 1990: first attempt to use computer
 Efforts continue

11. Why Automate?
 Improved safety
 Humans get tired, distracted;machines don’t
 Machines react faster
 Aviation automated before HLM
 Worst distraction scenario: reservoir empties,
pump air into patient
 Would you still need a person dedicated to
running HLM?

12. This Project
 Computer control of HLM
 Monitor Volume in venous reservoir
 Control speed of arterial pump
 Goal: do not allow reservoir level to drop
below critical level
 Proof of concept/feasibility study
 Description of possible next steps

13. Automated heart-lung machine
Reservoir
Autopilot
Arterial pump
Heat Heater-cooler
exchanger
Oxygenator Arterial filter

14. Test automated HLM

15. This Project: Technique
 Monitoring reservoir:
 Measure volume by weighing reservoir
 Suspend reservoir from strain gage
 Computer polls strain gage
 Control pump speed:
 Pump has connection for external control by
another pump (master-slave)
 Connect to D/A converter in computer
 Computer plays part of master

16. This Project – strain gage

17. Monitoring reservoir volume
 Why use this method?
 No blood contact
 Does not require modifying reservoir
 Easily adaptable to different bag reservoirs
 Other types of reservoirs have issues

18. Monitoring reservoir volume
 Tested three ways
 Maximum accuracy
 Effect of flow and vibration on accuracy
 Sensitivity to change in volume
 The tests cover patients from a small adult
female using a Cardiac Index of 1.8 to a
very large adult male using a Cardiac
index of 2.4

19. Cardiac Index
 Method of indexing blood flow to patient
size
 Size measured by Body Surface Area
 Calculated from height, weight
 E.g., CI 2.4 means 2.4 LPM per M2

20. This Project – simulated patient

21. Maximum accuracy
 Fill reservoir using graduated cylinder
 100ml to capacity in 100ml increments
 Strain gage reads to 0.01 Kg = 10ml
 Capacity is 1200ml
 Record value from strain gage
 Do three times to check repeatability

22. Maximum accuracy - Results
 Largest absolute error 0.01 Kg
 Largest percent error : 2.5 %
 0.01 Kg at 400ml
 Volumes < 400ml no error

23. Flow and Vibration
 Build basic circuit
 Use another reservoir to simulate patient
 Add different volumes to circuit
 1500ml to 3000ml
 500ml Increment
 Circulate at different flow rates
2 LPM to 7 LPM
 1 LPM increment

24. Flow and Vibration
 Take multiple readings from strain gage
 0.5 second interval
 Check variations in readings
 Results:
 Largest variation 0.03 Kg (1.12 to 1.15 Kg)
 Mostly variation 0.01
 Conclusion:
 Flow and vibration no effect on accuracy

25. Sensitivity to change
 Circulate at different flow rates
2 to 7 LPM, 1 LPM increment
 Fully or partially occlude input to reservoir
 Take readings of strain gage
 0.5 sec interval
 5 seconds
 Determine correlation coefficient

26. Sensitivity to change - Results
 Correlation coefficient: -0.91 to -1.00

27. Sensitivity to change – worst
Full occl. 4 LPM (67 ml/ sec)
1.5
1.45
1.4
1.35
1.3
1.25
1.2
1.15
1.1
1.05
1
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Ti m Seconds
e

28. Sensitivity to change – best
Full Occl. 7 LPM (120 ml/ sec)
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Ti m Seconds
e

29. Monitoring Reservoir -
Summary
 This method of monitoring volume is as
good as or better than standard of practice
which is the perfusionist reading the
volume from a scale on the side of
reservoir

30. Reservoir

31. Autopilot operator interface

32. Autopilot log
Max flow rate 1 LPM, min pct flow 50, low level 300, min level 100
700 1.2
600
1
500
0.8
reservoir level ml
400
flow rate LPM
Volume
0.6
Flowrate
300
0.4
200
0.2
100
0 0
1
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Time seconds

33. Demonstration
 Auto HLM demo

34. Overall results
 This method for automated control of a
heart-lung machine is feasible

35. Next steps
 How to build on this project
 Further automation of A-V circuit

36. Tasks – Part 1
 Modern pump
 Blood monitoring
 Gas flow and mixture
Reservoir
Autopilot
Arterial pump
Heat Heater-cooler
exchanger
Oxygenator Blood monitor Arterial filter

37. Modern pump
 Validate approach
 Tech support available
 Test over full range
 Stress test autopilot
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler
Oxygenator Blood monitor Arterial filter

38. Blood monitoring
 Inline, real-time
 PaO2, PaCO2, Sv02, Hgb
 Calc O2 consumption w/blood flow, show trend
 Tell if anesthesia wearing off
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler
Oxygenator Blood monitor Arterial filter

39. Gas flow and mixture
 Tighter control of blood gases
 Monitor gas/blood flow to O2 consumption ratio
 Detect impending oxygenator failure
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler
Oxygenator Blood monitor Arterial filter

40. Part 1 - result
 Key pieces automated
 Close attention of perfusionist
Reservoir
Autopilot
Arterial pump
Heat Heater-cooler
exchanger
Oxygenator Blood monitor Arterial filter

41. Tasks – Part 2
 Arterial line pressure
 Occluders
 Heater-cooler
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler ALP monitor
Oxygenator Blood monitor Arterial filter

42. Arterial line pressure
 Part of perfusionist scan
 High pressure requires stopping pump
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler ALP monitor
Oxygenator Blood monitor Arterial filter

43. Occluders
 Standard is scissor clamps
 Mainly used at initiation & termination
 Much to monitor
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler ALP monitor
Oxygenator Blood monitor Arterial filter

44. Heater-cooler
 Cool & rewarm blood w/heat exchanger
 From a few degrees to zero C
 Severe cooling means care rewarming
 Rewarm fast as possible without overheating
blood
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler ALP monitor
Oxygenator Blood monitor Arterial filter

45. Part 2 - result
 Allow autopilot to control initiation and
termination of bypass as well as monitor
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler ALP monitor
Oxygenator Blood monitor Arterial filter

46. Part 2 – Autopilot operator interface

47. Part 3 – voice recognition
 More convenient in OR than mouse and
keyboard
 Quicker access
 Multiple locations
 Bluetooth headset

48. Voice recognition
 Two types of commands
 Normal– repeated back for confirmation
 Emergency – immediate execution

49. Voice recognition
 Sample normal dialog
 Perf: “autopilot increase blood flow zero point
five”
 Auto: “increase blood flow zero point five”
 Perf: “yes”
 Auto: “blood flow now at five point zero”

50. Voice recognition
 Sample emergency dialog
 Perf:“autopilot emergency stop”
 Auto: “pump stopped, gas flow stopped”

51. Overall design guidelines
 Perfusionist ultimate safety device
 Equipment will fail
 Always manual backup
 Switch quick and simple

52. References
 1. Austin Jon W., Harner David L.. The Heart-lung Machine and Related Technologies of Open Heart Surgery. Phoenix: Phoenix Medical Communications1986:7.
 2. Chronicle of Aviation, JL International Publishing Inc., 1992:462
 3. C CRAFOORD, B NORBERG, and A SENNING. Clinical studies in extracorporeal circulation with a heart-lung machine. Acta Chir Scand, Mar 1957; 112(3-4): 220-45.
 4. F OLMSTED, WJ KOLFF, and DB EFFLER. Three safety devices for the heart-lung machine. Cleve Clin Q, Jul 1958; 25(3): 169-76.
 5. Murray N. Andersen, M.D., James F Ulrich,P.E.,Christian V. Mouritzen, M.D. An automatic flow control system for extracorporeal circulation. Journal of thoracic and
Cardiovascular Surgery, Aug 1965;50(2):260-264
 6. A KANTROWITZ, S REINER, and D ABELSON. An automatically controlled, inexpensive pump-oxygenator.J. Thorac. Cardiovasc. Surg., Nov 1959; 38: 586-93.
 7. VINCENT L. GOTT, ROBERT D. SELLERS, RICHARD A. DeWALL, RICHARD L. VARCO, and C. WALTON LILLEHEI. A Disposable Unitized Plastic Sheet
Oxygenator for Open Heart Surgery. Chest, Dec 1957; 32: 615 - 625.
 8. Pierre M. Galletti M.D.,Ph.D,Gerhard A. Brecher, M.D.,Ph.D.. HEART-LUNG BYPASS, Principles and Techniques of Extracorporeal Circulation. Grune &
Stratton,1962:199
 9. Gerald Moss M.D.,Ph.D. A device to maintain automatically and continuously an absolute or relative constant weight of a subject or container during perfusion. Surgery,
June 1961
 10 . F. John Lewis,M.D., Sidney J. Horwitz, B.S.,Joseph B. Naines,Jr.,B.S. Semiautomatic control for an extracorporeal blood pump. Journal of thoracic and
Cardiovascular Surgery,March 1962,43(3):392-396
 11. James J. Roche, Irving Ungar,M.D.,Herman S. Coleman,M.D. An electric apparatus for rapid and precise regulation of the venous blood-reservoir height on heart-lung
machines. Surgery, September 1964,56(3):561-564
 12. Jeffrey B. Riley, B.A. CCT. A Technique for Computer Assisted Monitoring in the Management of Total Heart-lung Bypass. The Journal of Extra-Corporeal Technology,
1981, 13(1):171-176.
 13. Thomas Hankins, C.L.A.,C.C.P. Computer Assisted Bypass Management. The Journal of Extra-Corporeal Technology, 1980, 12(4):95-102
 14. J.B. Riley, M.B. Hurdle, B.A. Winn, P.A. Wagoner. Automation of Cardiopulmonary Bypass Data Collection. The Journal of Extra-Corporeal Technology,1985, 17(1):7-
12
 15. D. Gaillard,MD, C. Barraud,CCP, O. Bical, MD, L. Detoni,CCP, L.S. Montejo,MD,A. Venetti,MD. Use of an Extracorporeal Circulation Workstation During the Routine
Care of Cardiac Patients. Int J Artif Organs,1990 Feb,13(2):35-41
 16. N. Chauveau, W. Van Meurs, R. Barthelemy, J.P. Morucci. Automatic modules for extracorporeal circulation control. Int J Artif Organs, 1990,13(10):692-696
 17. Toshiyuki Beppu, ME, Yasuharu Imai, MD, Yasuhiro Fukui, PhD. A Computerized control system for cardiopulmonary bypass. The Journal of Thoracic and
Cardiovascular Surgery, 1995, 109(3):428-438
 18. US Patent No 7022099, A. Kenneth Litzie et al. Extracorporeal blood handling system with automatic flow control and methods of use. File: Mar 17, 2003, Issue: Apr 4,
2006
 19. Alfred H Stammers, Brian L Mejak.An update on perfusion safety: does the type of perfusion practice affect the rate of incidents related to cardiopulmonary bypass?.
Perfusion, 2001, 16:189-198
 20. Bryan V. Lich,CCP, D. Mark Brown, CCP. The Manual of Clinical Perfusion. Perfusion.com, Inc. 2004
 21. Glenn P. Gravlee MD, Richard F. Davis MD, Mark Kurusz CCP, Joe R. Utley MD. Cardiopulmonary Bypass Principles and Practice, second edtion. Lippincott Williams
& Wilkins 2000.
 22. Bryan V. Lich, CCP,D. Mark Brown CCP. The Manual of Clinical Perfusion, Second Edition Updated. Perfusion.Com 2004:47
 23. Glenn P. Gravlee MD, Richard F. Davis MD, Mark Kurusz CCP, Joe R. Utley MD. Cardiopulmonary Bypass Principles and Practice, second edtion. Lippincott Williams
& Wilkins 2000: 88
 24. Bryan V. Lich, CCP, D. Mark Brown CCP. The Manual of Clinical Perfusion, Second Edition Updated. Perfusion.Com 2004:71
 25. Bryan V. Lich, CCP, D. Mark Brown CCP. The Manual of Clinical Perfusion, Second Edition Updated. Perfusion.Com 2004:79

53. Acknowledgement
 Cardiovascular Science/Perfusion
department MWU Glendale, AZ